Fix #28120, strong mode allows field overrides

pkg/analyzer/lib/src/dart/element/element.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2503 matching lines @@
    */
   static String _REQUIRED_CLASS_NAME = "Required";
 
   /**
    * The name of the top-level variable used to mark a parameter as being
    * required.
    */
   static String _REQUIRED_VARIABLE_NAME = "required";
 
   /**
-   * The name of the top-level variable used to mark a member as intended to be
-   * overridden.
-   */
-  static String _VIRTUAL_VARIABLE_NAME = "virtual";
-
-  /**
    * The element representing the field, variable, or constructor being used as
    * an annotation.
    */
   Element element;
 
   /**
    * The compilation unit in which this annotation appears.
    */
   CompilationUnitElementImpl compilationUnit;
 
@@ skipping 88 matching lines @@
   @override
   bool get isRequired =>
       element is ConstructorElement &&
           element.enclosingElement.name == _REQUIRED_CLASS_NAME &&
           element.library?.name == _META_LIB_NAME ||
       element is PropertyAccessorElement &&
           element.name == _REQUIRED_VARIABLE_NAME &&
           element.library?.name == _META_LIB_NAME;
 
   /**
-   * Return `true` if this annotation marks the associated member as supporting
-   * overrides.
-   *
-   * This is currently used by fields in Strong Mode, as other members are
-   * already virtual-by-default.
-   */
-  bool get isVirtual =>
-      element is PropertyAccessorElement &&
-      element.name == _VIRTUAL_VARIABLE_NAME &&
-      element.library?.name == _META_LIB_NAME;
-
-  /**
    * Get the library containing this annotation.
    */
   Source get librarySource => compilationUnit.librarySource;
 
   @override
   Source get source => compilationUnit.source;
 
   @override
   DartObject computeConstantValue() {
     if (evaluationResult == null) {
@@ skipping 1606 matching lines @@
 
   /**
    * Set whether this field is static.
    */
   void set isStatic(bool isStatic) {
     _assertNotResynthesized(_unlinkedVariable);
     setModifier(Modifier.STATIC, isStatic);
   }
 
   @override
-  bool get isVirtual {
-    for (ElementAnnotationImpl annotation in metadata) {
-      if (annotation.isVirtual) {
-        return true;
-      }
-    }
-    return false;
-  }
+  bool get isVirtual => true;
 
   @override
   ElementKind get kind => ElementKind.FIELD;
 
   @override
   /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/ > visitor) =>
       visitor.visitFieldElement(this);
 
   @override
   AstNode computeNode() {
@@ skipping 4825 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }